1. Field of the Invention
The present invention relates to a light transmission type vacuum separating window for separating a vacuum area into a plurality of vacuum areas through a film that transmits the light of a wavelength range such as an X-ray range and an infrared ray range and to a soft X-ray transmitting window as well.
2. Related Background Art
In recent years, with an advancement of a high integration technology of electronic devices and semiconductors, a demand is to probe substance properties and physical phenomena in micro-areas by effecting hyperfine working. For probing the substance properties and physical phenomena in the micro-areas by the hyperfine working, synchrotron radiation rays and free electron laser beams are coming into a practical use. The synchrotron radiation rays and the free electron laser beams are defined as electromagnetic waves emitted in a direction of tangential line of a trajectory when the traveling direction of the electrons or positive electrons travelling at a velocity approximate to the speed of light velocity is deflected by a magnetic field generated by a deflection magnet. It is feasible to take out the electromagnetic waves of an X-ray range including a soft X-ray from an infrared ray range with a high intensity. Further, the characteristic is that the light (electromagnetic waves) taken out is deflected. As described above, the light intensity is much higher than that of any other light source. Under such circumstances, an attempt is going to be made, wherein the synchrotron radiation rays and the free electron laser beams are, though impossible in the prior art, applied to the hyperfine working process technology and the ultra high sensitivity measuring technology. In addition, a superprecise measurement that has hitherto been impossible can be performed by use of polarization of light. The attempt to apply the synchrotron radiation rays and the free electron laser beams to these areas is therefore going to be effected.
Normally, the synchrotron radiation rays and the free electron laser beams are taken into the atmosphere from a take-out window. The synchrotron radiation rays and the free electron laser beams are employed for the hyperfine working process technology, the ultra high sensitivity measuring technology and the superprecise measurement. By the way, in the above-described hyperfine working process technology, ultra high sensitivity measuring technology and superprecise measurement each using the synchrotron radiation rays and the free electron laser beams, the points at issue are an attenuation of light intensity and a distortion of polarized light in the window for taking out the synchrotron radiation rays and the free electron laser beams. Especially, the X-ray of the soft X-ray area is easily absorbed by a material of this window when passing through the window. Hence, there arises a problem that the light intensity is conspicuously attenuated. Further, when performing the superprecise measurement about substance properties or the like, the problems are the attenuation of light intensity and the distortion of polarized light in the light transmitting windows of a light source and of a detector. Besides, the synchrotron radiation rays and the free electron laser beams have high intensities. This presents a problem, wherein the window for taking out the light tends to be damaged by the radiation rays, particularly by the heat.
On the other hand, an accelerator serving as a light source of the synchrotron radiation rays and the free electron laser beams accelerates the electrons and positive electrons up to a velocity approximate to the speed of light. It is therefore required that the trajectory of the electrons or the positive electrons be in an ultra high vacuum on the order of 10.sup.-9 Torr (1.33.times.10.sup.-7 Pa) or greater to prevent the electrons and positive electrons from colliding with gas particles and resultantly disappearing or scattering midway. Besides, in a beam line for taking out the soft X-rays in a synchrotron radiation ray facility, particularly the X-ray of the soft X-ray range is easily absorbed by a gas in the vacuum. Since the light intensity is largely attenuated, it is required that a soft X-ray transmitting range be in an ultra high vacuum of the order of 10.sup.-7 Torr (1.33.times.10.sup.-5 Pa) or more. Then, the soft X-ray is taken out of this ultra high vacuum area by employing the soft X-ray transmitting window, with a lithography transfer device serving as a light source. A helium atmosphere on the order of 1013.3 mb is provided in this transfer device. A rise in temperature of a mask that is derived from an irradiation of radiant rays is prevented so as not to cause a distortion of a mask. Even in the helium atmosphere on the order of 1013.3 mb, an attempt to reduce a pressure of helium in the device is executed because of a large attenuation of the soft X-ray.
Further, the electromagnetic waves of the synchrotron radiation rays have continuous spectra and a high intensity and are therefore applied to a physicochemical analysis such as a structural analysis and a state analysis. A study for obtaining information that could not be obtained so far is going to be performed. In a soft X-ray detector employed for such analyses, a soft X-ray transmitting window for separating an ultra high vacuum area from a pressure reduction gas area is needed in a detection part of the detector having a pressure reduction gas as in, e.g., a gas-flow type detector.
Paying attention to the fact that the synchrotron radiation ray has a high intensity, other studies are also on the verge of practice, wherein a film deposition and substrate etching are performed by utilizing a photochemical reaction between the electromagnetic waves of the soft X-ray area and a gas substance. In this type of photochemical reaction device, the film deposition and etching are effected under depressurization in most cases. The soft X-ray transmitting window for separating the ultra high vacuum area from the pressure reduction gas area is needed when introducing the soft X-ray into the device via the beam line.
As described above, there is demanded the soft X-ray transmitting window for separating the ultra high vacuum area from the vacuum area such as the pressure reduction area with a highly efficient transmission of the X-ray of the soft X-ray area without attenuation, wherein baking necessary for attaining a further ultra high vacuum is performable.
As shown in a magazine ([Applied Physics], Vol. 5 (published in 1986) p. 494), a conventionally manufactured apparatus is constructed as follows. A beryllium foil serving as a soft X-ray transmitting window constructive member is joined to an opening of an ultra high vacuum flange by methods such as soldering and electron beam welding. An airtightness is thus kept. Alternatively, after joining to a window frame of copper, etc. has been conducted by the same method, this is fixedly welded to the ultra high vacuum flange to hold the airtightness. Metal beryllium, however, has a high melting point but exhibits poor properties in terms of ductility and malleability. Hence, a breakdown such as a crack may easily occur in the beryllium foil in the method of directly welding to well-utilized stainless steel as an ultra high vacuum material. Then, as disclosed in Japanese Patent Laid-Open Publication No. 63-64253, titled [Soft X-Ray Take-Out Window], a member joined to a free oxygen copper plate by the diffused junction method is used as a gasket. Additionally, as disclosed in Japanese Patent Laid-Open Publication No. 63-273100 , titled [Soft X-Ray Take-Out Window Structure and Manufacturing Method thereof], the following method is proposed. A beryllium foil having a thickness of 200 .mu.m is airtightly soldered to the stainless steel. Thereafter, cracking in the beryllium foil when welded is prevented by reducing the thickness of the soft X-ray transmitting area with physicochemical process working.
Further, as disclosed in Japanese Patent Laid-Open Publication No. 1-276550, titled [Soft X-ray Take-Out Window and Manufacturing Method thereof], the following method is also proposed as a method of avoiding the stress generated during a welding process. A metal elastic member deformable in a direction parallel to an opening surface is soldered to the beryllium foil and the stainless steel, thus avoiding the stress. A durability of the beryllium foil is thereby improved. The diffused junction method, the electron beam welding and the soldering as employed above, however, present such problems that beryllium starts being recrystallized enough to decrease the intensity because of heating beryllium at 700.degree. C. or more. Deterioration and cracking are both occur easily. Then, a method of keeping the airtightness without heating the beryllium foil is proposed. As disclosed in Japanese Patent Laid-Open Publication No. 1-9400, titled [Soft X-Ray Take-Out Window], the airtightness is kept by use of a fluorine rubber O-ring as an elastic member vacuum sealing medium. In this method, however, it is necessary to apply a force enough to keep the airtightness on the elastic member and the beryllium foil as well. It is difficult to reduce a thickness of the beryllium foil.
In addition, as disclosed in Japanese Patent Laid-Open Publication No. 2-272399, titled [Soft X-Ray Take-Out Window] and Japanese Patent Laid-Open Publication No. 2-272400, titled [Soft X-Ray Take-Out Window], there are proposed methods of keeping the airtightness by use of a metals exhibiting a predetermined consistency and vapor pressure characteristic in place of the O-ring. It is also difficult to reduce the thickness of the beryllium foil because of enhancing the airtightness by applying the force on the beryllium foil. Then, the following method is proposed. As disclosed in Japanese Patent Laid-Open Publication No. 3-128499, titled [Radiation Ray Transmitting Thin Film Manufacturing Method and Radiation Ray Transmitting Window Having Radiation Ray Transmitting Thin Film Manufactured by the Same Method], a beryllium film is vacuum-deposited on free oxygen copper without using the beryllium foil. Thereafter, the free oxygen copper of the window member is etched by use of concentrated nitric acid. The beryllium film of 20 .mu.m is thus obtained. The airtightness of the thus formed soft X-ray transmitting window constructive member is held by employing the fluorine rubber O-ring.
As explained above, a large variety of X-ray transmitting windows have been proposed, wherein the ultra high vacuum is kept by separating the atmospheric pressure area from the ultra high vacuum area. It is, however, difficult in terms of reliability to reduce the thickness of the beryllium foil or beryllium film down to 20 .mu.m or less in order to separate the atmospheric pressure area from the ultra high vacuum area. Hence, this leads to a difficulty to efficiently transmit the soft X-ray because of a large absorption of the soft X-ray in the transmitting window.
By the way, some attempts are conducted presently, wherein the attenuation of the X-ray of the soft X-ray range is prevented by use of a thin film composed of silicon nitride, silicon carbide, boron nitride, diamond, etc. A film as thin as several .mu.m-0.1 .mu.m can be formed. For example, in the case of an X-ray having an energy of 1 kev, conventionally employed beryllium having a thickness of 20 .mu.m exhibits a transmittance of 11%. Contrastingly, a boron nitride thin film having a thickness of 1 .mu.m exhibits a transmittance of 65%. A silicon nitride thin film having a thickness of 1 .mu.m shows a transmittance of 51%. Further, in the case of an X-ray having an energy of 500 eV, beryllium having a thickness of 20 .mu.m exhibits a transmittance of 6.times.10.sup.-7 %. In contrast, the 1 .mu.m boron nitride thin film has a transmittance of 7.8%. The 1 .mu.m silicon nitride thin film has a transmittance of 2.1%. A highly efficient transmission of the soft X-ray is obtained. It is therefore possible to employ the thin films composed of silicon nitride, silicon carbide, boron nitride, diamond, etc. as a soft X-ray transmitting thin film member.
FIG. 24 is a sectional view illustrating a structure of the above-mentioned conventional soft X-ray transmitting thin film member. Referring to FIG. 24, a soft X-ray transmitting thin film 32 is supported on a support substance 31. Speaking of sizes of these components, for example, the support substance 31 has a diameter of 40 mm; a transmitting part has a diameter of 20 mm; and the soft X-ray transmitting thin film 32 has a thickness of 1 .mu.m. Generally, for simplicity of manufacturing, the support substance 31 is composed of silicon, while the soft X-ray transmitting thin film 32 is formed of a silicon nitride thin film. The thus constructed soft X-ray transmitting thin film member is joined to an ultra high vacuum structure of stainless steel or an aluminum alloy. For this purpose, the soldering and the electron beam welding involve difficulty. Then, an attempt to use an epoxy resin is going to be made.
Further, in connection with an infrared ray transmitting window, as shown in, e.g., p.372 of [Applied Spectroscopy Hand Book] (published by Asakura Shoten, 1984), an infrared ray detector is exemplified. The infrared ray transmitting window has a thickness of several mm for separating the vacuum on the side of the infrared ray detector from the atmosphere. In addition, materials employed for this infrared ray transmitting window are potassium bromide or cesium bromide having a long wavelength limit in the majority of cases as reported in the magazine ([Applied Physics] Vol. 5 (published in 1986) p. 492).
Further, a substrate temperature when forming the film is required to be precisely controlled in the film forming process of a semiconductor or the like. Proposed with this necessity is a radiation thermometer in which the infrared ray transmitting window involves the use of zinc selenide (ZnSe) having a very large transmission area in the film forming processor.
This film forming process of the semiconductor requires the precise control of the film thickness when forming the film. Therefore, the film forming processor is mounted with an ellipsometer for measuring a thickness of the formed film.
In addition, as shown in, e.g., [UHV COMPONENTS technical data] "UHV Viewports and viewport Shutters" (published by VACUUM GENERATORS Co., Ltd), a visible ray transmitting window is constructed by fusing, to a flange member, a window material such as a glass plate, a quartz plate, a sapphire plate, etc.
The conventional soft X-ray transmitting thin film member is thus constructed, and hence the epoxy resin classified as an organic substance easily undergoes a deterioration in radiation relative to the X-ray. The conventional soft X-ray transmitting thin film member presents a problem with respect to a long-term reliability. Moreover, the epoxy resin decompose easily at a high temperature. The epoxy resin is decomposed during a baking process conducted for obtaining an ultra high vacuum, with the result that a gas is evolved.
Additionally, the conventional infrared ray transmitting window has a problem. The substances such as potassium bromide and cesium bromide are vulnerable to moisture. A careful treatment is needed for dewing or the like caused by cooling of the detector.
A further problem is that zinc (Zn) and selenium (Se) of zinc selenide used for the window material are high of vapor pressure; and these elements are taken in as impurities during sample manufacturing.
The conventional infrared ray transmitting window presents the problems as described above. The materials are confined to those having a high transmittance of the infrared ray. Therefore, the careful treatment is needed. In addition, where the infrared ray transmitting window material contains substances having a high vapor pressure, these substances are taken in as impurities when manufacturing the sample.
Furthermore, the conventional visible ray transmitting window has the following problems. The stress is applied on the window material enough to cause double refraction. Besides, there has been practiced the method of keeping the airtightness of the window material such as the glass plate, the quartz plate and the sapphire plate by the O-ring or the like. However, it is necessary to apply enough force to keep the airtightness on the window material such as the glass plate, the quartz plate and the sapphire plate. The stress acts on the window material, with result that the double refraction is produced.
Further, in conventional ellipsometer also, the precise measurement is difficult because of such a defect that the above-described double refraction is caused.
Moreover, the vacuum ultraviolet transmitting window also presents the same problems as those of the infrared ray transmitting window and the visible ray transmitting window.
Further, in the conventional light transmitting window, it is difficult in terms of reliability to set the thickness of the light transmitting window constructive member to 20 .mu.m or less in order to separate the atmospheric pressure area from the vacuum area. For this reason, it is difficult to efficiently transmit the soft X-ray and the infrared ray because of the large absorption of the soft X-ray and the infrared ray in the transmitting window. The absorption of the infrared ray, etc. in the transmitting window is large. Hence, there arises such a problem that materials for the light transmitting window constructive member are limited. Additionally, the distortion and scatter of light in the transmitting window are reduced with difficulty.
Employed are the methods of fusing the window material to the flange member and keeping the airtightness by the O-ring. Consequently, the problem is caused, wherein the stress is applied on window material enough to cause the double refraction.
The following are additional problems. The synchrotron radiation rays and free electron laser beams have the high intensities. Hence, the window for taking out the light easily undergoes damage by the radiation ray, especially by the heat. The window tends to be damaged during the baking process for obtaining the ultra high vacuum.